1. Field of the Invention
The present invention is in the field of microelectronics and specifically relates to an electrically alterable non-volatile switch or gate for use in selectively interconnecting microcircuit elements formed on a wafer.
2. The Prior Art
In U.S. Pat. No. 3,940,740, issued Feb. 24, 1976, and assigned to the assignee of the present application, Coontz describes a powerful method for providing reconfigurable microelectronic circuit devices through the use of a permanently alterable but non-volatile switching device. That patent was primarily concerned with the application of such a device, and its detailed design was not described at length.
The ability to achieve the full-wafer, discretionary wiring described in the Coontz patent has been impeded due to the lack of an economical switching device to permit interconnection of the operable microcircuit elements on the wafer and the disconnection of the defective elements. Attempts to use MNOA (Metal Nitride Oxide Semiconductor) transistors alone to perform the inteconnection function have been unsatisfactory due to the relatively high impedance of the device. Thus, when a number of microcircuit elements were interconnected to form a chain, the series impedance of the MNOS transistors attenuated the signals to unsatisfactory levels.
In U.S. Pat. No. 3,660,827, issued May 2, 1972, Tickle shows a bistable electrical circuit, such as a flip-flop, incorporating insulated-gate field-effect transistors as non-volatile memory elements. Comparable devices are also shown in: U.S. Pat. No. 3,636,530, issued Jan. 18, 1972 to Mark, et al; in U.S. Pat. No. 3,549,911, issued Dec. 22, 1970 to Scott, Jr.; and in U.S. Pat. No. 3,500,142, issued Mar. 10, 1970, to Kahng.
Generally, such bistable circuits were regarded as useful mainly as non-volatile elements of a computer memory. None of the above references, it is believed, suggests the use of such bistable circuits in electrically active interconnect means for selectively connecting microelectronic circuits formed on the same wafer as the bistable devices.